Gas generator for an occupant protection system of a vehicle

ABSTRACT

A gas generator for an occupant protection system of a vehicle includes a compressed gas store, first and second bursting devices, and a gas generating triggering device. The compressed gas store has a discharge opening and is configured to store a compressed gas. The first bursting device can close the discharge opening. The triggering device can open the discharge open. The bursting devices can be supported against one another when the compressed gas store is closed, and an increased pressure for bursting a bursting device being able to be built up between the bursting devices by gas generated by the triggering device.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This is a continuation of International Application PCT/DE2004/000814,which has an international filing date of Apr. 14, 2004 (incorporated byreference herein). The International Application was not published inEnglish, but was published in German as WO 2004/094200 A1 (incorporatedby reference herein).

BACKGROUND

The invention relates to a gas generator for an occupant protectionsystem of a vehicle.

Gas generators for occupant protection systems in vehicles are used tofill gas sacks with gas and to inflate them for protecting occupants inthe event of an accident. Depending on the region of use of the gassack, it is desirable for the gas pressure in the gas sack to bemaintained over a relatively long period of time, in particular over anumber of seconds. This is necessary in particular in the case of gassacks used for side protection, since an overturning of a vehiclegenerally lasts for a certain period of time within which the gas sackis to be filled in order to protect the impact of the occupants. Such along useful life can be achieved with a cold gas generator, in which acold compressed gas is used as the filling gas. By contrast, the hotgases generated by a pyrotechnic gas generator would lead, due to theirrapid cooling, to a similarly rapid drop in pressure within the gassack.

Cold gas generators generally have a compressed gas store in which thestored compressed gas is stored under high pressure. In order to openthe compressed gas store, use is generally made of a pyrotechnic solidexplosive charge which can supply a contribution at the same time forfilling the gas sack. This then involves what are referred to as hybridgas generators.

A secure closure of the compressed gas store even in the case of highoutside temperatures and a rapid and reliable opening of the compressedgas store in the event of being triggered is essential for the reliableuse of these gas generators.

A hybrid gas generator of this type is disclosed, for example, in DE 19951 672 A1 (hereby incorporated by reference herein in its entirety). Acompressed gas store is closed here in a gas-tight manner by a burstingdisk. The bursting disk is supported counter to the internal pressure ofa container on a supporting device which can be partially destroyedand/or moved by the pressure arising during the combustion of apyrotechnic solid explosive charge.

SUMMARY

One embodiment of the invention relates to a gas generator for anoccupant protection system of a vehicle. The gas generator comprises acompressed gas store, which has a discharge opening and is configured tostore a compressed gas; a first bursting device which closes thedischarge opening; a second bursting device; and a gas generatingtriggering device configured to open the discharge opening. The burstingdevices being supported against one another when the compressed gasstore is closed, and an increased pressure for bursting a burstingdevice being able to be built up between the bursting devices by gasgenerated by the triggering device.

Another embodiment of the invention relates to a gas generator for anoccupant protection system of a vehicle. The gas generator comprises acompressed gas store, the compressed gas store including a dischargeopening and is configured to store a compressed gas; a bursting devicewhich closes the discharge opening; and a triggering device for openingthe discharge opening. The bursting device is supported on at least onesupporting band when the compressed gas store is closed, and thetriggering device acts upon the supporting band in order to burst thebursting device.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become apparent from the following description, appendedclaims, and the accompanying exemplary embodiments shown in thedrawings, which are briefly described below.

FIG. 1 shows a sectional illustration through a gas generator in theregion of the discharge opening of a compressed gas store according toan embodiment of the invention.

FIG. 2 shows a sectional illustration through a gas generator in theregion of the discharge opening of a compressed gas store, the dischargeopening being closed by two bursting devices and a cavity being formedbetween the bursting devices according to an embodiment of theinvention.

FIG. 3 shows a sectional illustration of a gas generator in the regionof the discharge opening of a compressed gas store with two burstingdevices which are supported against one another via a spacer elementaccording to an embodiment of the invention.

FIG. 4 shows a sectional illustration through a further gas generator inthe region of the discharge opening of a compressed gas store, in whichgas from a triggering device can flow first of all into an antechamberaccording to an embodiment of the invention.

FIG. 5 shows a sectional illustration through a gas generator in theregion of the discharge opening of a compressed gas store, with agas-generating propellant being arranged between two bursting devicesaccording to an embodiment of the invention.

FIG. 6 shows a sectional illustration through a gas generator in theregion of the discharge opening of a compressed gas store, with abursting device being supported here via a supporting band according toan embodiment of the invention.

DETAILED DESCRIPTION

It is an object of the present invention to specify an improved gasgenerator with a compressed gas store, in which the compressed gas storecan be securely closed and can be opened with a rapid reaction.

The gas generator, of embodiments of the invention, has a compressed gasstore, which has a discharge opening and is intended for storing acompressed gas, the discharge opening being closed by a bursting deviceand a gas-generating triggering device being provided for opening thedischarge opening. According to embodiments of the invention, at leastone further bursting device is provided, the bursting devices beingsupported against one another when the compressed gas store is closed,and, in order to burst a bursting device, an increased pressure beingable to be built up between the bursting devices by means of the gasgenerated by the triggering device.

The basic idea of embodiments of the invention is therefore to close thecompressed gas store by means of at least two bursting devices. Thebursting devices can be designed in particular as bursting disks orother membranes. By means of a suitable definition of the strengthvalues, in particular by the selection of material, the thickness andgeometry of the bursting devices, said bursting devices are designed insuch a manner that they can only together withstand the internalpressure of the compressed gas store. As a consequence of this, when afirst bursting device is destroyed, the other bursting devices are alsodestroyed under the internal pressure of the compressed gas store. Thedestruction of at least one bursting device therefore results in theopening of the compressed gas store.

The destruction of a first bursting device is achieved according to anembodiment of the invention by an increased pressure being able to bebuilt up between the bursting devices by means of the gas generated bythe triggering device. The pressure of the gas generated by thetriggering device and in addition that part of the internal pressure ofthe compressed gas store which is transmitted by the inner burstingdevices to the outer bursting device therefore act on the outer of thebursting devices. By contrast, the internal pressure of the compressedgas store minus the increased pressure of the gas generated by thetriggering device and minus the application of force to the outerbursting devices acts on the inner bursting devices. When a criticalpressure built up by the triggering device is reached, the outermostbursting device will therefore burst first. The inner bursting devices,on account of their design, can then no longer withstand the internalpressure of the compressed gas store and likewise burst. The compressedgas store is thus opened. This results firstly in a secure closure ofthe compressed gas store by the at least two bursting devices andsecondly in an efficient and rapid opening of the compressed gas store.

In order to be able to reliably and efficiently build up an increasedpressure between at least two bursting devices, a cavity isadvantageously formed between the at least two bursting devices, inwhich cavity an increased pressure can then be built up by means of thegas generated by the triggering device. In order to form the cavity,according to an embodiment, the two bursting devices are supportedagainst one another via a spacer element, since, inter alia, thedimensioning of the cavity can be set in a simple manner via the spacerelement.

The gas generated by the triggering device is advantageously conductedbetween the at least two bursting devices via a gas line. In acost-effective variant, this gas line is integrated directly in aretaining device retaining the bursting devices. This retaining devicecan furthermore be integrated directly in the housing of the compressedgas store, so that here, by shaping of the housing of the compressed gasstore, the retaining device for the bursting devices and the gas linefor conducting the gas generated by the triggering device can beproduced at the same time.

A simple assignment of the triggering device to the compressed gas storeis achieved by a gas outlet opening of the triggering device beingarranged directly opposite the gas line, with it being possible forthere to be a gap between the gas outlet opening and the gas line. Sincethe gas of the triggering device emerges from the gas outlet opening athigh velocity, the gas jet thus produced can be aimed directly into thegas line. A direct connection of the gas outlet opening to the gas lineis therefore not required. By this means, the installation of the gasgenerator can be considerably simplified. In a further variant, it isalso possible, however, to connect the gas outlet opening to the gasline in a sealing manner.

If the gas of the triggering device is to be used at the same time forfilling a gas sack, then it is appropriate to allow the triggeringdevice to flow directly into an antechamber and then to conduct the flowfrom this antechamber into the gas line. The pressure built up in theantechamber by the triggering device can then continue to be used forfilling a gas sack.

A particularly compact structural size of the gas generator is achieved,in a development of the embodiment, by a gas-generating propellant ofthe triggering device being provided between the bursting devices. Thegas-generating propellant may be situated either over the entire regionof the discharge opening of the compressed gas store or only in asubregion between the bursting devices. The bursting devices can besupported against one another in particular also via the propellant. Inorder to be able to achieve the most efficient use possible of the gasproduced by the propellant or to be able to use as little propellant aspossible, it is appropriate to close the cavity situated between thebursting devices in an essentially gas-tight manner. By means of thisembodiment, in which a propellant of the triggering device is situatedbetween the bursting devices, a very compact structural size of the gasgenerator can be achieved. The structural size is determined essentiallyonly by the expansion of the compressed gas store. The triggering deviceis then situated essentially in the closure of the discharge opening ofthe compressed gas store.

The gas generator of an embodiment has a compressed gas store, which hasa discharge opening and is intended for storing a compressed gas, thedischarge opening being closed by a bursting device and a triggeringdevice for opening the discharge opening being provided. According tothe embodiment, the bursting device is supported on at least onesupporting band when the compressed gas store is closed, with thetriggering device acting upon the supporting band in order to burst thebursting device.

In a first embodiment, the supporting band can be fixed on the gasgenerator at at least two opposite ends. The triggering device then actsupon the supporting band between the two fixed ends in such a mannerthat the supporting band is severed by the triggering device. Thesupporting band can be severed in particular by means of a hot gas jetfrom the triggering device.

In a second variant embodiment, the supporting band is fixed on the gasgenerator at one end and in the triggering device at its opposite end.The supporting band in the triggering device can be released from thetriggering device in order to open the discharge opening. This can takeplace, for example, by means of a suitable mechanism.

After the supporting band is severed, the internal pressure of thecompressed gas store presses on the bursting device in such a mannerthat the latter bursts. The bursting device and the supporting bandtherefore open up the discharge opening of the compressed gas store. Inorder to achieve secure supporting of the bursting device, thesupporting band, in an advantageous refinement, is guided in aslotted-guide mechanism. This slotted-guide mechanism may be integrated,for example, in the retaining device for the bursting device. Securesupporting of the bursting element can be achieved by the supportingband completely covering the bursting element over the entire region ofthe discharge opening. In a more cost-effective variant, the supportingband only partially covers the bursting device in the region of thedischarge opening.

The bursting device is in turn designed in such a manner that itwithstands the internal pressure of the compressed gas store only whensupported on the supporting band.

The invention is explained in more detail below with reference to thedrawings of the figures.

FIG. 1 shows, in a sectional illustration, a cut-out of a gas generatoraccording to an embodiment of the invention. A compressed gas store inthe form of a compressed gas cylinder 1 with a housing 11 is filled witha compressed gas which serves, when the gas generator is triggered, toact upon, for example, a gas sack. Provided in the housing 11 of thecompressed gas cylinder 1 is a discharge opening 100 from which thecompressed gas stored in the compressed gas cylinder 1 can bedischarged. This discharge opening is closed by two bursting devices inthe form of membranes 2, 3. The two membranes 2, 3 are supported on oneanother and, in the embodiment shown in FIG. 1, are curved outward bythe internal pressure prevailing in the compressed gas cylinder 1.

The two membranes 2, 3 are configured in such a manner that they canonly together withstand the internal pressure prevailing in thecompressed gas cylinder 1. By contrast, a single one of the twomembranes 2, 3 cannot withstand the internal pressure and bursts underthe applied pressure. Only by the two membranes 2, 3 being supportedagainst one another can a reliable sealing of the compressed gascylinder 1 be achieved.

The two membranes 2, 3 are retained in a retaining device 12 which isfastened to the housing 11 of the compressed gas cylinder 1. A gas-tightclosure of the interior of the compressed gas cylinder 1 is thusachieved by the two membranes 2, 3, with the actual seal being achievedby the membrane 2 directed in the direction of the interior.

A gas supply line 10 is provided in the retaining device 12 and can beused to conduct a gas generated by a triggering device 5 (indicateddiagrammatically) between the two membranes 2, 3. The triggering device5 has, in particular, a pyrotechnic propellant and is used fortriggering the gas generator. Use can be made here, for example, of aknown solid gas generator as triggering device 5.

The gas generated in the triggering device 5 escapes via an opening 51in the triggering device. This opening 51 is arranged opposite the gasline 10, so that the gas flows in a targeted manner into the gas line 10at a high discharge velocity. In the process, an air gap 53 between theopening 51 and the gas line 10 can also be bridged. Gas line 10 andopening 51 are therefore not closed off by each other in a gas-tightmanner.

A gas-tight closure, in which the opening is closed off by the gas linein a directly sealing manner, is provided in a development (notillustrated here) of the embodiment shown in FIG. 1.

An increased pressure can be built up between the two membranes 2, 3 bythe gas of the triggering device via the gas line 10. When this pressurereaches a critical level, one of the two membranes 3 bursts, as a resultof which the remaining membrane 2 is then acted upon by the fullinternal pressure of the compressed gas cylinder 1. Under this internalpressure the second membrane 2 also collapses, so that the dischargeopening 100 of the compressed gas cylinder 1 is opened.

The opening of the discharge opening 100 is therefore achieved here by acombination of two membranes, which cannot withstand the internalpressure of the compressed gas cylinder on their own, and by themembranes additionally being acted upon by a gas generated by atriggering device. In this case, first of all one of the two membranes2, 3 is destroyed by the gas provided by the triggering device,whereupon the second membrane also collapses due to the internalpressure prevailing in the compressed gas cylinder 1.

A development of this principle is shown in FIG. 2. Here, in turn, acompressed gas cylinder 1 is closed by two membranes 2, 3. The innermembrane 2 is retained in such a manner in a retaining device 12, whichis integrated in the housing 11 of the compressed gas cylinder 1, thatit only comes into contact with the second membrane 3 after asignificant curvature. By means of a different configuration of themembranes 2, 3, in particular with respect to their radii, theirmaterial and/or their thickness, different curvature structures of oneor two membranes 2, 3 can therefore be obtained. Owing to the curvature,a cavity 23 is produced between the two membranes. This cavity is closedin an essentially gas-tight manner and, in the exemplary embodimentshown in FIG. 2, communicates via a gas line 10 with a triggering device5 which is connected directly to the latter.

The opening of the discharge opening 100 of the compressed gas cylinder1 is achieved in turn by an increased pressure being built up betweenthe two membranes 2, 3 by the gas generated in the triggering device 5.The gas generated in the triggering device 5 passes via the gas duct 10into the cavity 23 situated between the two membranes 2, 3. An increasedpressure rapidly builds up here and acts both on the outer membrane 3and on the inner membrane 2. A pressure which is composed of theinternal pressure of the compressed gas cylinder 1 minus the pressurebuilt up in the cavity 23—i.e. a reduced pressure—therefore acts on theinner membrane. The increased pressure built up in the cavity 23 by thegas flowing into it plus that part of the internal pressure of thecompressed gas cylinder 1 which is transmitted by the membrane 2—i.e. anincreased pressure—acts on the outer membrane 3. The outer membrane 3will therefore usually collapse first. Then, after the cessation of thesupport by the outer membrane 3, the inner membrane 2 is fully actedupon by the internal pressure acting in the compressed gas cylinder 1and is therefore likewise destroyed. The discharge opening 100 istherefore opened.

FIG. 3 shows a development of the embodiment shown in FIG. 2. The twomembranes 2, 3 are supported against one another here via spacer element4 which may be designed, for example, as a spacer disk or spacer ring.As a result, the cavity 23 formed between the two membranes 2, 3 isincreased or the curvature of the inner membrane 2 is reduced. Thedesired volumes for the cavity 23 between the two membranes 2, 3 canthus be set via the dimensioning of the spacer element 4.

FIG. 4 shows a further refinement of a gas generator according to anembodiment of the invention. A compressed gas cylinder 1 is arranged ina housing 9 of the gas generator, with it being possible for the housing9 to be pulled in a simple manner over the compressed gas cylinder 1.The compressed gas cylinder 1 is in turn closed by two membranes 2, 3which are supported against one another via a spacer element 4. Gas canflow into the cavity 23 situated between the two membranes 2, 3 via agas line 10 situated in the housing 11 of the compressed gas cylinder 1.

The housing 9 has a chamber 90 into which the gas generated by thetriggering device 5 can flow. Gas generated by the triggering device 5can flow into the gas line 10 from the chamber 90 via an opening 91 inthe chamber 90, which opening is situated opposite the opening of thegas line 10. In the process, an air gap situated between the opening 91in the chamber 90 and the gas line 10 is

bridged, since the gas flows in a targeted manner out of the opening 91into the gas line 10 at a high discharge velocity.

The required positive pressure in the cavity 23 between the twomembranes 2, 3 is therefore achieved owing to the high dischargevelocity of the gas out of the opening 91 of the chamber 90. Themembranes 2, 3 are destroyed in the manner already described and thedischarge opening 100 of the compressed gas cylinder 1 is opened.

FIG. 5 shows a development of the gas generator according to anembodiment of the invention. The discharge opening 100 in a compressedgas cylinder 1 is in turn closed in a gas-tight manner via two membranes2, 3. The membranes are in turn retained in a gas-tight manner in aretaining device 12 which is fixed on the housing 11 of the compressedgas cylinder 1. In this embodiment, a propellant 55 of the triggeringdevice is arranged between the two membranes 2, 3. The propellant 55 canextend here either over the entire area between the two membranes 2, 3,or else can extend only in a subregion, in particular a ring, betweenthe two membranes 2, 3.

The two membranes 2, 3 can therefore be supported against one anothervia a propellant 55 which is designed as a solid body. Igniting contacts56 are in direct contact with the propellant 55, with the ignitingcontacts being guided here through the retaining device 12.

In order to open the discharge opening 100, the propellant 55 is nowignited via the igniting contacts 56, as a result of which a gas isproduced in the intermediate space 23 between the two membranes 2, 3.This gas builds up an increased pressure in the cavity 23 leadingultimately, according to the known principle, to the destruction of thetwo membranes 2, 3. The two membranes are also designed here in such amanner that they only together withstand the internal pressure of thecompressed gas cylinder 1.

A development of an embodiment of the invention is shown in FIG. 6.Here, a compressed gas cylinder 1 is closed by a membrane 2 which isconnected in a retaining device 12 in a gas-tight manner to the housing11 of the compressed gas cylinder 1. The membrane 2 in turn isconfigured in such a manner that it cannot withstand the internalpressure of the compressed gas cylinder 1 on its own. The membrane 2 istherefore supported via a supporting band 8. The supporting band 8extends here either over the entire area of the discharge opening 100,or else only over a subregion of this area. The supporting of themembrane 2 on the supporting band 8 enables the internal pressure of thecompressed gas cylinder 1 to be absorbed.

The supporting band 8 is fixed on the housing of the gas generator attwo opposite ends 80, 81 and conducts the forces exerted on thesupporting band 8 by the membrane into the housing of the gas generator.The supporting band 8 is guided here in a slotted-guide mechanism 13which is provided in the retaining device 12. In order to open thedischarge opening 100, the supporting band is severed by the triggeringdevice 50. For this purpose, a hot gas jet which emerges from an outletopening 52 of the triggering device 50 is directed at the supportingband 8.

If the supporting band 8 is severed, it slips out of the slotted-guidemechanism on account of the internal pressure of the compressed gascylinder 1, with the membrane 2 being acted upon at the same time by thefull internal pressure. The membrane 2 is therefore destroyed and thedischarge opening 100 opened up.

The German Priority Application 103 18 888.6, filed Apr. 17, 2003,including the specification, drawings, claims and abstract, isincorporated by reference herein in its entirety.

Given the disclosure of the present invention, one versed in the artwould appreciate that there may be other embodiments and modificationswithin the scope and spirit of the invention. Accordingly, allmodifications attainable by one versed in the art from the presentdisclosure within the scope and spirit of the present invention are tobe included as further embodiments of the present invention. The scopeof the present invention is to be defined as set forth in the followingclaims.

1. A gas generator for an occupant protection system of a vehiclecomprising: a compressed gas store, which has a discharge opening and isconfigured to store a compressed gas; a first bursting device whichcloses the discharge opening; a second bursting device; and a gasgenerating triggering device configured to open the discharge opening,wherein the bursting devices being supported against one another whenthe compressed gas store is closed, and an increased pressure forbursting a bursting device being able to be built up between thebursting devices by gas generated by the triggering device.
 2. The gasgenerator as claimed in claim 1, wherein the bursting devices which aresupported against one another are configured so that only together thebursting devices withstand the internal pressure of the compressed gasstore.
 3. The gas generator as claimed in claim 1, further comprising acavity formed between the bursting devices, wherein increased pressurecan be built up in the cavity by the gas generated by the triggeringdevice.
 4. The gas generator as claimed in claim 3, wherein in order toform the cavity, the bursting devices are supported against one anothervia a spacer element.
 5. The gas generator as claimed in claim 3,wherein the first bursting device has a geometry different from thesecond bursting device such that the radii of the first bursting deviceis different from the radii of the second bursting device, and whereinthe different geometries of the bursting device form the cavity.
 6. Thegas generator as claimed claim 3, wherein the cavity is closed in anessentially gas-tight manner and can be acted upon by the gas generatedby the triggering device only via a gas supply line.
 7. The gasgenerator as claimed in claim 6, wherein the gas supply line is providedin a retaining device configured to retain the bursting devices.
 8. Thegas generator as claimed in claim 7, wherein the retaining device isintegrally formed with the housing of the compressed gas store.
 9. Thegas generator as claimed in claim 6, wherein the gas supply line isconnected directly to a gas outlet opening of the triggering device. 10.The gas generator as claimed in claim 6, wherein a gas outlet opening ofthe triggering device is arranged opposite the gas line with a gapthrough which the gas can escape being present between the gas outletopening and the gas line.
 11. The gas generator as claimed in claim 6,wherein the gas supply line is connected to the triggering device via anantechamber arranged in the housing of the gas generator.
 12. The gasgenerator as claimed in claim 1, further comprising at least onegas-generating propellant of the triggering device, the propellant beingarranged between the bursting devices.
 13. The gas generator as claimedin claim 12, wherein the bursting devices are supported against oneanother via the propellant.
 14. The gas generator as claimed in claim12, wherein the cavity situated between the bursting devices is closedin an essentially gas-tight manner.
 15. The gas generator as claimed inclaim 12, further comprising igniting contacts configured to ignite thepropellant, the igniting contacts are guided through a retaining deviceconfigured to retain the bursting devices.
 16. The gas generator asclaimed in claim 1, wherein the bursting devices are formed bydestructible membranes.
 17. The gas generator as claimed in claim 16,wherein the discharge opening of the compressed gas store is closed in agas-tight manner by at least one of the membranes.
 18. A gas generatorfor an occupant protection system of a vehicle comprising: a compressedgas store, the compressed gas store including a discharge opening and isconfigured to store a compressed gas; a bursting device which closes thedischarge opening; and a triggering device for opening the dischargeopening, wherein the bursting device is supported on at least onesupporting band when the compressed gas store is closed, and thetriggering device acts upon the supporting band in order to burst thebursting device.
 19. The gas generator as claimed in claim 18, whereinthe supporting band is fixed on the gas generator at at least twoopposite ends.
 20. The gas generator as claimed in claim 19, wherein thetriggering device acts upon the supporting band between the fixed endsand the supporting band is capable of being severed by the triggeringdevice.
 21. The gas generator as claimed in claim 20, wherein a gas jetfrom the triggering device is configured to sever the supporting band.22. The gas generator as claimed in claim 18, wherein one end of thesupporting band is fixed on the gas generator and an opposite end of thesupporting band is releasably fixed on the triggering device.
 23. Thegas generator as claimed in claim 18, further comprising a slotted-guidemechanism provided on a retaining device for the bursting device, theslotted-guide mechanism being configured to guide the support band. 24.The gas generator as claimed in claim 18, wherein the supporting bandonly partially covers the bursting device in the region of the dischargeopening.
 25. The gas generator as claimed in claim 18, wherein thesupporting band completely covers the bursting device in the region ofthe discharge opening.
 26. The gas generator as claimed in claim 18,further comprising a second bursting device, the bursting devices beingsupported against one another.
 27. The gas generator as claimed in claim18, wherein the bursting device comprises a membrane configured to sealoff the discharge opening.
 28. The gas generator as claimed in claim 18,wherein the bursting device is configured to withstand the internalpressure of the compressed gas store only when supported on thesupporting band.